Process and apparatus for cooling gaseous mixtures



M. FRANKL Feb. 11, 1936.

PROCESS AND APPARATUS FOR COOLING GASEOUS MIXTURES Filed July 19, 1932 M M m M y r m m a w .F. N 2 m u m 5 H m 5: NM i MM w z: w W 0 n w 5 i M .j s M 1 A1 w INVENTOR Mir/m9; firi/v/rz BY m fiTTORNEYS Patented Feb. 11, 1936 UNITED STATES- PATENT OFFICE PROCESS AND APPARATUS Fon cooLmo oasrzousmx'runns Mathias Frank], Augsburg, Germany, nor to American Oxythermic Corporation, New York, N. Y., a corporation oi? Delaware Application July 19, 1932, Serial No. 623,345:

to separation intocomponents and includes correlated improvements and discoveries whereby such separations are enhanced.

In the separation of gaseous mixtures through liquefaction and rectification, it is particularly advantageous in order to cover cold losses to cool the gaseous mixture or the air, or one of the separation products directly from atmospheric temperature, or from the temperature of cooling water to nearly the liquefaction temperature in an expansion engine. Thus, with air, a temperature reduction from about +20 C. to -175 C. or lower is necessary. If this temperature drop is to be obtained with performance of work in an expansion engine, then the air to be expanded must be compressed to 250 atmospheres gauge. The pressures herein are all to be understood as gauge and not absolute pressures. It is also to be understood that specific reference herein to air is merely illustrative and not in a limiting sense.

The economy of gas separation processes may be improved by forecooling the compressed air or gas to -40 C. by means of an ammonia refrigerating machine, whereby the desired low cooling may be obtained with an operating pressure, in an expasion engine, of about 144 atmospheres. Forecooling by means of an ammonia refrigerating machine does not permit oil lubrication of the engine cylinders and the pistons cannot be made tight with respect to the cylinder walls by means of metallic piston rings. It is necessary, accordingly, to use a material which, even without lubrication, does not cause corrosion of the cylinder walls, for example, leather washers. This type of piston packing, such as leather washers is, how-v ever, 'unsuitable for high operating pressures because the washers do not make sufiicientlytight joints, or wear out prematurely,

It is-an object of the invention to provide a process wherein the necessity of operating at high.

pressures with the attendant disadvantages is obviated.

Another object of the invention is to provide a process for the separation of gaseous mixtures in which losses of cold are reduced or entirely covered.

A further object of the invention is to obtain cooling of the gaseous mixture to a low temperature at a relatively low pressure.

An additional object is to provide a process whereby a gaseous mixture cooled to substantially liquefyins; temperature by successive comi Cl. 52-123) pressions and expansions and in conjunction with which accumulated depositions of frost in a cold exchanger are prevented. A process is also provided whereby the temperature or a gaseous mixture may be lowered to substantially the liquea iaction point in an emcient, practical andeconomically successful manner.

It is also an object o! the invention to provide an apparatus which is adapted to accomplish the foregoing objects through a lowering of the tem- 10 perature of a gaseous mixture bymeans of combinations or compressors and expansion engines, whereby a plurality of compressions and expansio'ns is permitted.

Other objects of the invention will in part be it obvious and will in part appear hereinafter.

The invention accordingly comprmes the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, com- 20 binations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope oi the invention will be indicated in the claims. 25

In the practice of the invention the desired low cooling is obtained in an expansion" engine with lower operating pressures by compressing either twice the amount of a gaseous mixture, or a given amount of such a mixture twice to a pressure which is the square root of the pressure which 0 would be required ii the gas were compressed by a single compression as a simple unitary quantity. For example air, under the conditions of the invention, would therefore be compressed, with i'orecooling to -40 C. to the square root of 144, or 12 atmospheres. Thus, instead of compressing 100 cubic meters of air to 144 atmospheres and expanding it in two stages to one atmosphere in an expansion engine, two portions of air of 100 cubic meters each may be compressed to 12 atmospheres and each portion expanded in a separate cylinder in an expansion engine. Thus a gaseous mixture may be compressed, cooled, expanded, warmed, again compressed, then cooled to a lower temperature than that in the first instance, and expanded. More particularly, the process includes compressing air and cooling first by heat exchange with the cold content of a body of air which had been compressed, cooled by indirect heat exchange in a refrigerating machine, and further cooled by expansion, and then by expansion with external work.

a An apparatus in which the practice of the process may be accomplished includes in combination a two-cylinder compressor, a water cooler,

an ammonia refrigerating machine, a heat ex-.

changer, and a two-cylinder expansion engine.

In accordance with the. procedure of the invention, a first portion of air (100 cubic meters) is compressed to 12 atmospheres and forecooled to C. by means of an ammonia refrigerating machine. The compressed air is then expanded in a first cylinder of an expansion engine to one atmosphere, and thereby cooling practically to -l30 C. may be attained.

A second portion of air (100 cubic meters) likewise compressed at 12 atmospheres, is now forecooled to about 125 C. by means of a mutual exchange of heat with the cold content of the first portion of air cooled as above set forth to about -130 C., and then expanded in a second cylinder of the expansion engine whereby cooling proceeds to about -l75 C.

If the pressure is increased to 15 atmospheres, cooling to about l90 C. may be reached. At pressures up to 15 atmospheres, leather washers may be used as piston packing and last, as experlence has shown, a few months in continuous operation. In this manner, the machine can be operated without lubrication of the cylinders. With compression to from 12 to 15 atmospheres the moisture is removed from the air to the extent of 85 percent by the subsequent H2O cooling. The residual 15 percent must be removed before the air is ledinto the expansion engine. This removal is occasioned in the ammonia vaporizer in which the compressed air is cooled to about -40 C. This cooling may also be effected only with the first portion of air, the second portion being cooled by means of the first portion from +20 to -125 C. in a heat exchanger. In this case the moisture would freeze out in the heat exchanger, which is undesirable because defrost ing of the exchanger entails loss of cold and interruption of operation, whereas in the ammonia vaporizer this boar-frost can be removed very' simply by reversal whereby the vaporizer alternately operates as a condenser.

According to the preferred procedure, a portion of air is compressed in a first cylinder of a compressor and expanded in a first cylinder of an expansion engine. The expanded air serves in a heat. exchanger for forecooling a second portion of air which waspreviously dehydrated in the ammonia vaporizer and is now sucked in by a second cylinder of the compressor. The second cylinder of the compressor thus always contains dry air, which cannot cause a stoppage in the heat exchanger by the formation of hoar-frost. This air is again compressed in the second cylinder, then passed through a cooler to remove heat due to compression, cooled in the heat exchanger by mutual exchange with air expanded in the first cylinder of the expansion engine, expanded in a second cylinder of the engine, and conducted at a temperature of about -175 C. to a separation apparatus.

The accompanying drawing shows diagrammatically an illustrative embodiment of an-apparatus in which the procedural steps of the invention may be carried out. The apparatus comprises in combination a two-cylinder compressor moval of the heat of compression by means of Y cooling water in water cooler 5, the air is forecooled in an ammonia vaporizer 4 to -40 C. and is led into cylinder III of an expansion engine '2, there expanded to atmosphericpressure,

whereby it is further cooled to 130C. The thus cooled air is then led up through exchanger 3 wherein an exchange of heat, with air likewise compressed to from 12 to 15 atmospheres but cooled only to the temperature of the cooling water is effected, and it again becomes warmed to +15 C. The warmed air is now led into cylinder 9 of the compressor I, in which it is again compressed to from 12 to 15 atmospheres. It is then forecooled to C. in pipe-coil 12 and led into cylinder ll of the. expansion engine, whereby it is cooled .to l75 C. or lower, and at thistemperature passes from the engine at l3 and is conducted to an air liquefier or a resolution plant, not shown. The outlet N from the cooling coil in the ammonia vaporizer serves to effect removal of deposit duringdefrosting.

By the foregoing process it will be apparent that a gaseous mixture may have its temperature effectively lowered almost to the liquefaction point by simple compressions to relatively low pressures, followed by expansion to substantially -atmospheric pressure in an expansion engine limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

I claim:

1. In a process for cooling a gaseous mixture, the improvement which comprises compressing a gaseous mixture, cooling, expanding with external work, warming, again compressing, then cooling to a temperature lower than thatin the first instance, and expanding with external work.

2. In a process for cooling air prior to separation into components, the improvement which comprises compressing air to about 12 to 15 atmospheres, removing heat of compression, cooling to about 40 C., expanding with external work to about atmospheric pressure, passing in mutual countercurrent cold exchange relation with warm compressed air, again compressing to about 12 to 15 atmospheres, then passing in countercurrent cold exchange relation with expanded air at an initial temperature of about C., and expanding it again to about atmospheric pressure with external work.

.3. An apparatus comprising in combination a two-cylinder compressor, an ammonia vaporizer, a conduit connecting said compressor with a coil within said vaporizer and having a water cooler therein, a heat exchanger,. 9. two-cylinder expansion engine, a conduit connecting said ammonia vaporizer with one cylinder of said expansion engine, conduits connecting one cylinder of 8,080,509 said compressor with said heat exchanger, one

of said conduits passing through a water cooler and connecting with the coil of said heat exchanger, and another 01 said conduits connecting with the outer, space thereof, and conduits connecting the cylinders of said expansion engine. with the coil and outer space of said heat exchanger.

4. In a process for cooling a gaseous mixture prior to separation into components, the improvement which comprises compressing a gaseous mixture, cooling, further cooling in succession by expanding with external work, then cooling the gaseous mixture compressed a second time by heat exchange with such expanded cold gas, and further cooling the thus cooled compressed gaseous mixture by an expansion with external work.

5. In a process for cooling air prior to its separation into components, the improvement which comprises compressing air, cooling in an ammonia machine, further cooling in succession by expansion with external work, and then cooling air compressed a second time by heat exchange with the expanded cold air, and further cooling the thus cooled compressed air by an expansion with external work. I

6. In a process for cooling air prior to its separation into components, the improvement which comprises compressing air to about 12 to 15 atmospheres, cooling to about C. in an ammonia machine, further cooling in succession to a temperature of about C. by expansion,

and then cooling air again compressed to about 12 to 15 atmospheres by heat exchange with the. expanded cold air, and further cooling the thus cooled compressed air by an expansion with external work to about atmospheric pressure.

7. In a process for cooling a gaseous mixturev prior to separation into components, the improvement which comprises compressing a gaseous mixture, cooling said compressed mixture, then cooling the gaseous mixture compressed a second time by heat exchange with said first cooled mixture, and further cooling the thus cooled compressed gaseous mixture by an expansion with external work.

8. An apparatus comprising in combination a .two cylinder compressor, an ammonia vaporizer, a heat exchanger and a two cylinder expansion engine, a conduit connecting one cylinder of said compressor with the ammonia vaporizer and having a cooler therein, a conduit connecting said vaporizer with one cylinder of the expansion engine, conduits connecting the second cylinder of said compressor with the heat exchanger, and other conduits connecting the cylinders of the expansion engine with the heat exchanger, said conduits efiecting a passage of gaseous mixture to and fro between said compressor and heat exchanger and said expansion engine and heat exchanger.

9. An apparatus comprising in combination a two cylinder compressor, cooling means, a conduit connecting one cylinder of said compressor with said cooling means, means for effecting heat exchange mutually between cold expanded gaseous mixture and warm compressed gaseous mixture, a conduit connecting the second cylinder of said compressor with said heat exchange means, a two cylinder expansion enginel connected by means of a conduit with-said cooling means and by other conduits with said, heat exchange means whereby a gaseous mixture may be conducted from said cooling means to said expansion engine and to and fro between said expansion e gine and said heat exchange means. 

